A vehicle anti-roll system is a system designed to resist vehicle body roll motions or leans, for example, in a turn when a vehicle is steering or cornering. In a turn, lateral acceleration of the vehicle produces a lateral force at the centre of gravity. This lateral force creates a twisting force about the roll axis that leads to body roll or lean in the vehicle. One effect of the vehicle rolling or leaning is reduction in tire grip due to the positive camber of the wheels on the outside of the turn and negative on the inside. Thus, there is clearly a need for an anti-roll system to prevent or reduce the rolling or leaning of the vehicle.
Anti-roll systems provide two main functions. The first function is the reduction of body roll or lean. The reduction of body roll or lean is dependent on the total roll stiffness of the vehicle. Increasing the total roll stiffness of a vehicle does not change the weight transfer from the inside wheels to the outside wheels, it only reduces body lean. Another function of anti-roll systems is to tune the handling balance of a vehicle. The degree of understeer or oversteer can be tuned by changing the proportion of the total roll stiffness that comes from the front and rear axles. Increasing the proportion of roll stiffness at the front will increase the proportion of the total load transfer that the front axle reacts and decrease the proportion that the rear axle reacts. This will cause the outer front wheel to run at a comparatively higher slip angle, and the outer rear wheel to run at a comparatively lower slip angle, which is an understeer effect. Increasing the proportion of roll stiffness at the rear axle will have the opposite effect and decrease understeer.
The most common anti-roll system is a mechanical anti-roll bar, also known as a sway bar, a stabilizer bar, an anti-sway bar, a roll bar, or abbreviated as ARB. An anti-roll bar is a form of a torsion spring that stiffens or resists the roll of the vehicle. Anti-roll bars are usually constructed out of a U-shaped piece of metal, typically steel, that connects to the left and right sides of the suspension/wheels and at two mounting points in between. If the left and right wheels move together, the bar rotates about its mounting points and does not bend or twist and imparts no or negligible force to the respective wheels and suspension components. If the wheels move relative to each other, the bar is subjected to torsion and forced to twist. The bar resists the torsion through its strength or stiffness. The stiffer or stronger the bar, the more force required to move the left and right wheels relative to each other, which as a result, increases the amount of force required to make the vehicle roll.
One known problem with mechanical anti-roll bars is that the bar will transmit the force of one-wheel bumps to the opposite wheel because an anti-roll bar connects wheels on the opposite sides of the vehicle together. On rough or broken pavement, anti-roll bars can produce jarring, side-to-side body motions (a “waddling” sensation), which increase in severity with the diameter and stiffness of the anti-roll bars. Excessive roll stiffness, typically achieved by configuring an anti-roll bar too aggressively, will cause the inside wheels to lift off the ground during very hard cornering. This, of course, is only possible if the regular spring rate actually allows the outside wheels to handle the much increased load.
Another problem with mechanical anti-roll bars is that they are difficult or impossible to install on vehicles with abnormally shaped or sized hulls or chassis. As discussed above, a mechanical anti-roll bar is usually constructed out of a U-shaped piece of steel that connects to the left and right sides of the suspension and at two points in between. This may be difficult for vehicles that have abnormally shaped or sized chassis or hulls. Forcing a steel shape to conform to irregular hull or chassis shapes reduces that steel shape's stiffness, and the anti-roll bar becomes excessively heavy for its relative stiffness. With component weights having a direct effect on vehicle performance, including fuel economy, this is undesirable. For instance, some specialized vehicles have V-hulls. These V-hulls would require the shape of the anti-roll bar to be modified to go under or above the V-Hull, or for the V-hull to be outfitted with holes for allowing the anti-roll bar to pas through the V-hull. Either way, this process of outfitting and installing a mechanical anti-roll bar on an abnormally shaped vehicle or chassis, may be very difficult and expensive, or lead to additional design compromises. Thus, there is a need to create an anti-roll system that can be installed on various shapes of hulls and chassis, which can address, mitigate, or eliminate these design compromises and which can offer additional functionality and performance.
An additional problem with mechanical anti-roll bars is the inherent metallurgy of the anti-roll bars. Again, these metal U-shaped anti-roll bars are linked between the left and right wheels of a vehicle. With metal anti-roll bars, the metallurgy of the bars requires thicker and stronger bars to provide stiffer anti-roll forces, to ensure that the mechanical anti-roll bar does not yield due to torsional stress. These thicker or stronger bars inherently affect the articulation or wheel travel of the vehicle's suspension. Consequently, it very difficult, if not impossible to fine tune the anti-roll forces of a mechanical anti-roll bar for high articulation vehicles. For example, a high articulation vehicle might desire a certain amount of anti-roll resistance. If this desired anti-roll resistance is high, the vehicle will require a thicker, stronger anti-roll bar that will allow for enough articulation, leading to wheel liftoff during corning. If the full articulation of the vehicle is allowed by the anti-roll bar, the strength of the bar must be lowered. This results in less anti-roll forces which leads to oversteering or understeering. Thus, there is a need for an anti-roll system that can be fine tuned regardless of wheel articulation.
A further problem with mechanical anti-roll bar systems is that once they are installed it is difficult to bypass or turnoff the anti-roll feature of the bar without having to completely remove or mechanically disengage the U-shaped bar from the suspension/wheels of the vehicle. Some vehicles, for example, an off-road vehicle, may desire that an anti-roll system be engaged when traveling at high speeds on road, and may also desire the anti-roll system to be disengaged when traveling off-road. Thus, there is a need for an anti-roll system for a vehicle that may be bypassed or disengaged quickly and easily.
The instant invention is designed to address the above mentioned problems.